Secular Cooling Shapes Core–Mantle Heat Transfer and Mantle Plume Dynamics over 1.8 Billion Years

Petrological evidence and global heat budgets indicate that the solid Earth has cooled substantially over geological time, yet the influence of secular cooling on mantle dynamics in global 3D models remains poorly quantified. We incorporate secular cooling into 3D global mantle flow models using plate reconstructions extending back 1.8 billion years. The core-mantle boundary (CMB) temperature is modelled as decreasing over time in scenarios consistent with continuous outer-core dynamo action and inner-core crystallization. The internal heating rate is modelled as declining with radiogenic isotopes decay. By systematically varying convective vigour and core heat capacity, we demonstrate that secular cooling exerts a first-order control on deep mantle evolution. The CMB heat flux and the fractional area of Big LOwer-mantle Basal Structures (BLOBS) are strongly anti-correlated, highlighting slab–BLOBS interactions as central regulators of deep mantle heat transfer. Predicted plume heat flux broadly reproduces the long-term pattern of large igneous province eruptions. These results show that coupled core–mantle cooling is essential for reconstructing Earth’s thermochemical evolution over billion-year timescales and to link plume dynamics with geological observables.